1. Field of the Invention
The present invention relates to an auto focusing (AF) apparatus and an image inputting apparatus having the auto focusing apparatus, more specifically, to an improvement in an auto focusing apparatus provided with two auto focus means for carrying out auto focus operations of mutually different kinds.
2. Description of the Prior Art
Conventionally, an image inputting apparatus such as a still camera or video camera is provided with an AF apparatus for adjusting automatically and optimally a focusing state of an image of a subject. An AF apparatus in a typical image inputting apparatus for recording the image of subject on a recording medium such as film, video tape and so on as a photographic image or video picture includes a ranging means and an AF which is referred to as an outside light AF relative to a contrast AF as described hereinafter and which is adopted to control a focus driving means in such a manner that a lens is moved to a focus position corresponding to a distance obtained by the ranging means.
Here, the outside light AF is classified broadly into a passive AF and an active AF in accordance with a difference in a method ranged by the ranging means. The passive AF carries out the ranging based on phase contrast in a plurality of images of subject projected by the ranging means passing through an optical path different from an optical path passing through a photographic optical system and the active AF radiates, for example, near-infrared ray, ultrasound wave or the like to the subject to accomplish the ranging based on time or angle at which a reflected wave on the subject is returned to the ranging means.
On the other hand, in a new image inputting apparatus such as a electronic camera (digital camera) in which the image of subject is projected on an imaging means such as a CCD or CMOS through the photographic optical system and the projected image is taken out as an electric signal, the AF operation can be carried out by use of an image signal since the image is taken out as the image signal simultaneously with the projection of the image of subject.
In other words, in the AF operation, the contrast (sharpness and so on of image) of image projected in the imaging means is evaluated in real time based on the image signal for every movement of a focus lens in the photographic optical system while moving the focus lens, and the movement of the photographic optical system is stopped at the position that the evaluated value is maximum.
This is referred to as a contrast AF or a climbing contrast AF. This is also referred to as CCDAF in case of using a CCD as the imaging means.
The contrast AF has an advantageous effect that focusing accuracy is very high for carrying out AF operation evaluating an image which is actually projected on an imaging means is evaluated without obtaining a distance to the subject.
The more a repeated frequency in a series of operations, which are an accumulation of image, transfer, computation of evaluated value, and comparison, is increased, the more a focusing accuracy can be enhanced, because the contrast AF is carried out while comparing the evaluated value every each moved position of the focus lens.
On the other hand, there is a problem that when the repeated frequency is increased, it takes a long time until a focusing position is determined (completion of AF operation).
If a time (time lag) requiring from initiation of the AF operation to completion thereof is long, there is a case that photograph cannot be carried out at a predetermined timing because the AF operation is completed in a case of exerting important influential circumstance on focusing for the image of subject, for example, photographing a subject which moves at a high speed.
There is a case that in the contrast AF, it is not possible to carry out appropriate focusing operation because clear difference on the evaluated value is not appear in dark circumstance where the entire contrast is low.
On the contrary, the outside light AF is inferior to the contrast AF with respect to the focusing accuracy, but it is possible to follow relatively effectively to a dynamic subject and to prevent photograph timing from losing because the time lag requiring the operation of AF is small.
The outside light AF also has an advantageous effect that it is difficult to affect influence of the contrast of subject, usually.
Therefore, a hybrid AF (HBAF) is proposed, in which two AF means including an AF means carrying out the operation of the outside light AF and an AF means carrying out the operation of the contrast AF are provided to be changeable selectively these AF means in accordance with photograph or subject condition (see Japanese Patent Laid-Open No. 2001-255456).
However, when a user selects one of the AF operations in this technique, a selecting operation must be carried out always before either of the AF operations is selected.
In other words, for example, when a dynamic subject is photographed, a switching means such as a photographing-mode switching dial, switching button or the like is first operated to set the photographing mode into focusing speed priority mode corresponding to the outside light AF and then photographing is carried out.
On the other hand, it is required that when photographing is carried out to obtain accurate focusing, the switching means is first operated to set the photographing mode into focusing accurate priority mode corresponding to the contrast AF and then photographing is carried out.
It is noted that the aforementioned switching method for the AF operation has a good convenience because it is not necessary to carry out operation of switching the photographing mode point by point when multiple times of photographing are carried out continuously while maintaining the same photographing mode.
By the way, for example, during photographing in the focusing accurate priority mode in the AF apparatus, the dynamic subject comes suddenly within the user's range of vision. If the photographing is continued following to the dynamic subject, it is necessary that the user, first, operates the switching means so as to switch the AF operation to the focusing speed priority mode.
However, since the switching operation must be carried out even a case wishing to carry out the photographing by switching suddenly the AF operation, there is the possibility that it is not possible to obtain a desired image due to lose of photographing timing by taking time in the switching operation, lose sight of the subject by averting the user's eyes from the subject because of the switching operation.